1. Associate Professor, Dept. of Civil Engineering, Univ. de Oriente, Apartado Postal 4774, Puerto La Cruz 6023, Estado Anzoategui, Venezuela.
2. Professor of Environmental Engineering, Dept. of Civil Engineering, Univ. of Arkansas, 4190 Bell Engineering Center, Fayetteville, AR 72701.
3. Associate Professor of Environmental Engineering, Dept. of Civil Engineering, Univ. of Arkansas, 4190 Bell Engineering Center, Fayetteville, AR 72701 (corresponding author).